1. Field
The invention pertains to manufacturing of composite, sandwich-type panels comprising an outer layer of resinous binder and an inner core element or structural layer which is bonded to the outer layer. Such panels are useful in making walls, partitions, roofs, ceilings, floors, wall paneling, doors, signs, etc. In particular, the invention is directed to an improved method of making such composite panels.
2. State of the Art
Composite, sandwich-type panels have been produced having various type cores laminated to dense materials such as asbestos cement board, porcelained or enameled steel, aluminum, tempered glass, plywood, and perlite board. Generally, such sandwich constructions have been made by gluing sheets or panels of the external material to the broad, flat surfaces of preformed core elements.
It is also known to manufacture a composite, sandwich-type panel comprising an outer layer formed of a mixture of solid particles and a resinous binder, and a structural inner layer or core element which penetrates and is bonded to the outer resinous layer. In making such panels, a layer of a mixture of solid particles and a liquid resinous binder is spread on a mold base, and one side of the structural layer or core element is applied to the surface of the layer so as to penetrate the layer. The liquid binder in the layer is then cured to its hardened, rigid, solid state, thereby securely bonding structural layer or core element to the layer of cured resinous material. Such a process is described in U.S. Pat. No. 3,615,963.
It has been found difficult, however, when making the sandwich-type panels of U.S. Pat. No. 3,615,963, to maintain uniform penetration of the layer of particles and liquid resinous binder by the structural core element. This causes problems when the core element penetrates too deeply and disrupts the surface or otherwise mars the finish on the external surface of the panel. Further, it is very difficult to maintain a uniform thickness within a single panel as well as from one panel to another due to the varying depths that the structural core element penetrates into the layer of resinous material. Moreover, the strength of the bond between the outer layer and the structural core element will vary with the depth to which the core penetrates the layer of resinous material. It was proposed in U.S. Pat. No. 3,843,486 to alleviate the penetration problem by incorporating a support member in the form of a sheet material within the layer of the mixture of solid particles and liquid resinous binder. The support member was intended to regulate the depth to which the structural layer or core penetrates the layer of liquid resinous material. The process of U.S. Pat. No. 3,843,486 results in some improvement in the quality of the composite panels which are produced; however, experience has shown that it is still difficult to maintain uniform placement of the sheet of support material within the liquid layer of resinous material. For example, the sheet is often displaced from its intended position by the structural layer or core element during the manufacturing of the composite panel, which again results in nonuniformity in the thickness of the panels which are produced.
3. Objectives
The principal objective of the present invention is to provide an improved process for manufacturing composite panels such as those disclosed in U.S. Pat. Nos. 3,615,963 and 3,843,486, wherein substantial uniformity of thickness is obtained within each panel as well as from panel to panel, and wherein surface defects in the panels due to excessive penetration of the layer of resinous material which forms the exterior surface of the panel are essentially eliminated. Additional objectives are to provide a process with improved means for spreading the layer of resinous material on the mold base, and to provide improved steps for curing the resinous material and facilitating separation of the cured composite panel from the mold base.